It really depends on what you think is loud.
Warning, 50's will decrease your mileage...
I'm running dual 50s and hate it the majority of the time. The only times I don't is at idle where it sounds awesome, and WOT where it sounds like a bat out of hell. I've scared V-8 guys with it. Everytime I step on the gas, I grin because of the sound. My wife makes fun of me for it. That's why my mileage goes down.
But for cruising around town, it's pretty loud. Not obnoxious or anything, just loud and people are going to hear you. They have the typical flowmaster drove at 2000 RPM, just not as loud as 40s.
gotta61comet can comment on how they sound. Hopefully Big Al will be able too soon as well.
Oh...at 70MPH you can't hear them in the car at all. They like disappear except for a nice low, barely audible sound.
Slade